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Okay, this is going to be a very non-technical question ... so please bear with me. We have a hydro-air system, a Peerless Furnace and First Co (air return??). Our house is 1.5 yrs old. Recently, we've had a clunking noise reverberating from the basement which I have found to be in exact 6 hour intervals. What happens is one of the zones (we have 3) calls for heat, the furnace turns on, about 2 minutes later the furnace turns off with a whoosh and then across the room by the air handler there's a clunk. I've had our furnace repair guy here and he's disconnected the wires to the furnace from that zone and the noise doesn't happen. Then he tried disconnecting just from the thermostat and it still happens. He thinks there could be a crossed wire? But it doesn't make sense that something is timing this at exact 6 hour intervals. Any ideas, this is driving us crazy!!!!

I will take a stab at this one lol. You have a peerless boiler, first company a/h with hot water coil, correct? Not sure where you live and it doesnt matter, just couldnt believe that your still using heat.. If you have programable stats on other zones that may be calling for heat at that 6th hour, its possible that you have a bad zone valve (if you have one circulator) or you have a leaking or defective one way check on that zone causing water to enter that coil and turn on the blower on that zone????????? The fan may come on if the coil gets hot unless your fan control for heat is done by the stat and not water temp to that zone. Is the noise your hearing the duct making noise when the fan comes on?. Just a stab in the dark without being there myself..

Thanks for being so brave to reply to my issue. And you are correct my heat is off, but this is happening whether the thermostats are on heat, off or A/C. We've checked the programs on all the other zones and there's nothing set for that timeframe. The noise is like a pressure release. Once the furnace goes off, you hear like a hissing sound then across the room you hear like a pipe clunk. I will pass along your response to our repairman. If you can think of anything else, I'd appreciate it.

You keep saying furnace.. You mean the boiler right? Why does the boiler run? Do you have a tankless coil or indirect water tank off this boiler for your domestic hot water? The boiler is water not steam right? Oil or gas?

Sorry for being so clueless about this. Yes, it is a boiler. We have a separate (indirect?) water tank. And it's oil heat. The key to this is that it doesn't happen all the time. The boiler comes on to heat the water and when we had the heat on, it would come on to heat the house, this noise does not happen then. This noise ONLY happens at specific times at 6 hour intervals. It's so reliable I was able to get my repairman to hear it on cue! Is there anything else in this system aside from the thermostats that is timed? thanks again for the replies!

Patrice, there really isnt anything else "timed" like your explaing like the T-Stats in that system, that I could see from here lol. It sounds like the Indirect ( thats the name for a water heater or storage tank that doesnt have direct means of heating up like oil, gas, electric etcc) Its using the boiler water to exchange the heat to your domestic ( faucet water). There could be alot of things going on, but we just cant hear or see them lol. If you were the service tech, we could help you more. It could be water hammer, an air bleeder etc etc. You said he was there and heard this? He should know what it is, if not, maybe you need another set of eyes and ears down by your boiler.. When the pipes bang, do you feel and hear it at the sinks and in the walls etc? If your water heater has an oil burner firing into it, its not an indirect. If thats the case, turn off the boiler, (its just for heat) and see if the noise goes away.

You probably have a zone damper slamming shut or open in that zone that has been disconnected and the noise stops. And the 6 hour intervals might be due to the timer for fresh air that will cause the blower in the furnace to energize, the outside air damper to open, and all the 3 zone dampers to open (which would explain the noise)for total air flow throughout your home.

Have the tech run each zone damper open and closed to see if that is the noise.

"The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
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Originally posted by DeltaT You probably have a zone damper slamming shut or open in that zone that has been disconnected and the noise stops. And the 6 hour intervals might be due to the timer for fresh air that will cause the blower in the furnace to energize, the outside air damper to open, and all the 3 zone dampers to open (which would explain the noise)for total air flow throughout your home.

Have the tech run each zone damper open and closed to see if that is the noise.

That could be it Delta. With all this furnace and boiler talk, I didnt think they have a Zone damper system, and still dont know if they do. If thats the case, good read Delta.. It may even be the bypass damper if they have one.

Thanks for all your help. At this point I'll have to relay all these messages to our repairman and see what he thinks. At this point I think I know more than I ever wanted to know about our heating system .... and it's still not enough! But I appreciate all the help and I might be back on once I get some input from our repairman.